Comparison of Gain Properties with Electron--Electron and Electron--LO-Phonon Interactions in Quantum Cascade Structure

The gain properties of (AlN)_m/(GaN)_n superlattice-based quantum cascade structure are investigated by using a nonequilibrium Green's function (NGF) theory. In this theory, the electron--electron interaction and electron--LO-phonon interaction are both considered. The gain spectra of QCL are calculated from some current-driven items, which are derived from these two interactions. The results show that the effect of the electron--electron interaction is notable in the low-photon-energy range and the electron--LO-phonon interaction only takes effect in the high-photon-energy range, where photon energy is close to or larger than LO-phonon energy of GaN materials.